The electron configurations of seven elements of the Periodic Table are shown in Table 10.1. Which of the elements should have similar physical and chemical properties?

The string:
S7P2A22 (Identity - Chemical properties).
The math:
Pj Problem of Interest is of type identity. The Pj Problem of type grouping is also important because the problem is to determine groups of elements with similar chemical properties. However, the grouping is implicit in the identity of the elements. It is through the atomic numbers (identity) of the elements that one determines the valence-shell electrons which establish the properties of the elements.

Beryllium and Magnesium are metals that have the same number of valence-shell electrons and so should have similar chemical properties. Helium also has 2 valence-shell electrons but it is a gas and is usually grouped with the inert gases.

In general, elements with the same number of valence-shell electrons have similar physical and chemical properties. Also the group number of an element in the periodic table equals the number of its valence-shell electrons. Consequently, members of the same group have similar physical and chemical properties.